Diamondoid-containing low dielectric constant materials

ABSTRACT

Novel uses of diamondoid-containing materials in the field of microelectronics are disclosed. Embodiments include, but are not limited to, thermally conductive films in integrated circuit packaging, low-k dielectric layers in integrated circuit multilevel interconnects, thermally conductive adhesive films, thermally conductive films in thermoelectric cooling devices, passivation films for integrated circuit devices (ICs), and field emission cathodes. The diamondoids employed in the present invention may be selected from lower diamondoids, as well as the newly provided higher diamondoids, including substituted and unsubstituted diamondoids. The higher diamondoids include tetramantane, peritamantane, hexamantane, heptamantane, octamantane, nonamantane, decamantane, and undecamantane. The diamondoid-containing material may be fabricated as a diamondoid-containing polymer, a diamondoid-containing sintered ceramic, a diamondoid ceramic composite, a CVD diamondoid film, a self-assembled diamondoid film, and a diamondoid-fullerene composite.

REFERENCE TO RELATED APPLICATIONS

The present application is a divisional of application Ser. No.10/047,044, filed on Jan. 14, 2002 now U.S. Pat. No. 6,783,589 whichclaims the benefit of U.S. Provisional Patent Application No.60/262,842, filed Jan. 19, 2001; U.S. Provisional Patent Application No.60/348,032, filed Oct. 26, 2001; U.S. Provisional Application No.60/334,939, filed Dec. 4, 2001; and U.S. Provisional Patent ApplicationNo. 60/341,921, filed Dec. 18, 2001, which are incorporated herein byreference in their entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

Embodiments of the present invention are directed toward novel uses ofboth lower and higher diamondoid-containing materials in the field ofmicroelectronics. These embodiments include, but are not limited to, theuse of such materials as heat sinks in microelectronics packaging,passivation films for integrated circuit devices (ICs), low-k dielectriclayers in multilevel interconnects, thermally conductive films,including adhesive films, thermoelectric cooling devices, and fieldemission cathodes.

2. State of the Art

Carbon-containing materials offer a variety of potential uses inmicroelectronics. As an element, carbon displays a variety of differentstructures, some crystalline, some amorphous, and some having regions ofboth, but each form having a distinct and potentially useful set ofproperties.

A review of carbon's structure-property relationships has been presentedby S. Prawer in a chapter titled “The Wonderful World of Carbon,” inPhysics of Novel Materials (World Scientific, Singapore, 1999), pp.205-234. Prawer suggests the two most important parameters that may beused to predict the properties of a carbon-containing material are,first, the ratio of sp² to sp³ bonding in a material, and second,microstructure, including the crystallite size of the material, i.e. thesize of its individual grains.

Elemental carbon has the electronic structure 1s²2s²2p², where the outershell 2s and 2p electrons have the ability to hybridize according to twodifferent schemes. The so-called sp³ hybridization comprises fouridentical σ bonds arranged in a tetrahedral manner. The so-calledsp²-hybridization comprises three trigonal (as well as planar) σ bondswith an unhybridized p electron occupying a π orbital in a bond orientedperpendicular to the plane of the σ bonds. At the “extremes” ofcrystalline morphology are diamond and graphite. In diamond, the carbonatoms are tetrahedrally bonded with sp³-hybridization. Graphitecomprises planar “sheets” of sp²-hybridized atoms, where the sheetsinteract weakly through perpendicularly oriented π bonds. Carbon existsin other morphologies as well, including amorphous forms called“diamond-like carbon,” and the highly symmetrical spherical androd-shaped structures called “fullerenes” and “nanotubes,” respectively.

Diamond is an exceptional material because it scores highest (or lowest,depending on one's point of view) in a number of different categories ofproperties. Not only is it the hardest material known, but it has thehighest thermal conductivity of any material at room temperature. Itdisplays superb optical transparency from the infrared through theultraviolet, has the highest refractive index of any clear material, andis an excellent electrical insulator because of its very wide bandgap.It also displays high electrical breakdown strength, and very highelectron and hole mobilities. If diamond as a microelectronics materialhas a flaw, it would be that while diamond may be effectively doped withboron to make a p-type semiconductor, efforts to implant diamond withelectron-donating elements such as phosphorus, to fabricate an n-typesemiconductor, have thus far been unsuccessful.

Attempts to synthesize diamond films using chemical vapor deposition(CVD) techniques date back to about the early 1980's. An outcome ofthese efforts was the appearance of new forms of carbon largelyamorphous in nature, yet containing a high degree of sp³-hybridizedbonds, and thus displaying many of the characteristics of diamond. Todescribe such films the term “diamond-like carbon” (DLC) was coined,although this term has no precise definition in the literature. In “TheWonderful World of Carbon,” Prawer teaches that since most diamond-likematerials display a mixture of bonding types, the proportion of carbonatoms which are four-fold coordinated (or sp³-hybridized) is a measureof the “diamond-like” content of the material. Unhybridized p electronsassociated with sp²-hybridization form π bonds in these materials, wherethe π bonded electrons are predominantly delocalized. This gives rise tothe enhanced electrical conductivity of materials with sp² bonding, suchas graphite. In contrast, sp³-hybridization results in the extremelyhard, electrically insulating and transparent characteristics ofdiamond. The hydrogen content of a diamond-like material will bedirectly related to the type of bonding it has. In diamond-likematerials the bandgap gets larger as the hydrogen content increases, andhardness often decreases. Not surprisingly, the loss of hydrogen from adiamond-like carbon film results in an increase in electrical activityand the loss of other diamond-like properties as well.

Nonetheless, it is generally accepted that the term “diamond-likecarbon” may be used to describe two different classes of amorphouscarbon films, one denoted as “a:C—H,” because hydrogen acts to terminatedangling bonds on the surface of the film, and a second hydrogen-freeversion given the name “ta-C” because a majority of the carbon atoms aretetrahedrally coordinated with sp³-hybridization. The remaining carbonsof ta-C are surface atoms that are substantially sp²-hybridized. Ina:C—H, dangling bonds can relax to the sp² (graphitic) configuration.The role hydrogen plays in a:C—H is to prevent unterminated carbon atomsfrom relaxing to the graphite structure. The greater the sp³ content themore “diamond-like” the material is in its properties such as thermalconductivity and electrical resistance.

In his review article, Prawer states that tetrahedral amorphous carbon(ta-C) is a random network showing short-range ordering that is limitedto one or two nearest neighbors, and no long-range ordering. There maybe present random carbon networks that may comprise 3, 4, 5, and6-membered carbon rings. Typically, the maximum sp³ content of a ta-Cfilm is about 80 to 90 percent. Those carbon atoms that are sp² bondedtend to group into small clusters that prevent the formation of danglingbonds. The properties of ta-C depend primarily on the fraction of atomshaving the sp³, or diamond-like configuration. Unlike CVD diamond, thereis no hydrogen in ta-C to passivate the surface and to preventgraphite-like structures from forming. The fact that graphite regions donot appear to form is attributed to the existence of isolated sp²bonding pairs and to compressive stresses that build up within the bulkof the material.

The microstructure of a diamond and/or diamond-like material furtherdetermines its properties, to some degree because the microstructureinfluences the type of bonding content. As discussed in “Microstructureand grain boundaries of ultrananocrystalline diamond films” by D. M.Gruen, in Properties, Growth and Applications of Diamond, edited by M.H. Nazaré and A. J. Neves (Inspec, London, 2001), pp. 307-312, recentlyefforts have been made to synthesize diamond having crystallite sizes inthe “nano” range rather than the “micro” range, with the result thatgrain boundary chemistries may differ dramatically from those observedin the bulk. Nanocrystalline diamond films have grain sizes in the threeto five nanometer range, and it has been reported that nearly 10 percentof the carbon atoms in a nanocrystalline diamond film reside in grainboundaries.

In Gruen's chapter, the nanocrystalline diamond grain boundary isreported to be a high-energy, high angle twist grain boundary, where thecarbon atoms are largely π-bonded. There may also be sp² bonded dimers,and chain segments with sp³-hybridized dangling bonds. Nanocrystallinediamond is apparently electrically conductive, and it appears that thegrain boundaries are responsible for the electrical conductivity. Theauthor states that a nanocrystalline material is essentially a new typeof diamond film whose properties are largely determined by the bondingof the carbons within grain boundaries.

Another allotrope of carbon known as the fullerenes (and theircounterparts carbon nanotubes) has been discussed by M. S. Dresslehauset al. in a chapter entitled “Nanotechnology and Carbon Materials,” inNanotechnology (Springer-Verlag, New York, 1999), pp. 285-329. Thoughdiscovered relatively recently, these materials already have a potentialrole in microelectronics applications. Fullerenes have an even number ofcarbon atoms arranged in the form of a closed hollow cage, whereincarbon-carbon bonds on the surface of the cage define a polyhedralstructure. The fullerene in the greatest abundance is the C₆₀ molecule,although C₇₀ and C₈₀ fullerenes are also possible. Each carbon atom inthe C₆₀ fullerene is trigonally bonded with sp²-hybridization to threeother carbon atoms.

C₆₀ fullerene is described by Dresslehaus as a “rolled up” graphinesheet forming a closed shell (where the term “graphine” means a singlelayer of crystalline graphite). Twenty of the 32 faces on the regulartruncated icosahedron are hexagons, with the remaining 12 beingpentagons. Every carbon atom in the C₆₀ fullerene sits on an equivalentlattice site, although the three bonds emanating from each atom are notequivalent. The four valence electrons of each carbon atom are involvedin covalent bonding, so that two of the three bonds on the pentagonperimeter are electron-poor single bonds, and one bond between twohexagons is an electron-rich double bond. A fullerene such as C₆₀ isfurther stabilized by the Kekulé structure of alternating single anddouble bonds around the hexagonal face.

Dresslehaus et al. further teach that, electronically, the C₆₀ fullerenemolecule has 60 π electrons, one π electronic state for each carbonatom. Since the highest occupied molecular orbital is fully occupied andthe lowest un-occupied molecular orbital is completely empty, the C₆₀fullerene is considered to be a semiconductor with very highresistivity. Fullerene molecules exhibit weak van der Waals cohesiveinteractive forces toward one another when aggregated as a solid.

The following table summarizes a few of the properties of diamond, DLC(both ta-C and a:C—H), graphite, and fullerenes:

C₆₀ Property Diamond ta-C a:C-H Graphite Fullerene C—C bond length (nm)0.154 ≈0.152 0.141 pentagon: 0.146 hexagon: 0.140 Density (g/cm³)3.51 >3 0.9–2.2 2.27 1.72 Hardness (Gpa) 100 >40 <60 soft Van der WaalsThermal conduc- 2000 100–700 10 0.4 tivity (W/mK) Bandgap (eV) 5.45 ≈30.8–4.0 metallic 1.7 Electrical >10¹⁶ 10¹⁰ 10²–10¹² 10⁻³–1 >10⁸resistivity (Ω cm) Refractive Index 2.4 2–3 1.8–2.4 — —

The data in the table is compiled from p. 290 of the Dresslehaus et al.reference cited above, p. 221 of the Prawer reference cited above, p.891 a chapter by A. Erdemir et al. in “Tribology of Diamond,Diamond-Like Carbon, and Related Films,” in Modern Tribology Handbook,Vol. Two, B. Bhushan, Ed. (CRC Press, Boca Raton, 2001), and p. 28 of“Deposition of Diamond-Like Superhard Materials,” by W. Kulisch,(Springer-Verlag, New York, 1999).

A form of carbon not discussed extensively in the literature are“diamondoids.” Diamondoids are bridged-ring cycloalkanes that compriseadamantane, diamantane, triamantane, and the tetramers, pentamers,hexamers, heptamers, octamers, nonamers, decamers, etc., of adamantane(tricyclo[3.3.1.1^(3,7)] decane), adamantane having the stoichiometricformula C₁₀H₁₆, in which various adamantane units are face-fused to formlarger structures. These adamantane units are essentially subunits ofdiamondoids. The compounds have a “diamondoid” topology in that theircarbon atom arrangements are superimposable on a fragment of an FCC(face centered cubic) diamond lattice.

Diamondoids are highly unusual forms of carbon because while they arehydrocarbons, with molecular sizes ranging in general from about 0.2 to20 nm (averaged in various directions), they simultaneously display theelectronic properties of an ultrananocrystalline diamond. Ashydrocarbons they can self-assemble into a van der Waals solid, possiblyin a repeating array with each diamondoid assembling in a specificorientation. The solid results from cohesive dispersive forces betweenadjacent C—H_(x) groups, the forces more commonly seen in normalalkanes.

In diamond nanocrystallites the carbon atoms are entirelysp³-hybridized, but because of the small size of the diamondoids, only asmall fraction of the carbon atoms are bonded exclusively to othercarbon atoms. The majority have at least one hydrogen nearest neighbor.Thus, the majority of the carbon atoms of a diamondoid occupy surfacesites (or near surface sites), giving rise to electronic states that aresignificantly different energetically from bulk energy states.Accordingly, diamondoids are expected to have unusual electronicproperties.

To the inventors' knowledge, adamantane and substituted adamantane arethe only readily available diamondoids. Some diamantanes, substituteddiamantanes, triamantanes, and substituted triamantanes have beenstudied, and only a single tetramantane has been synthesized. Theremaining diamondoids are provided for the first time by the inventors,and are described in their co-pending U.S. Provisional PatentApplications Nos. 60/262,842, filed Jan. 19, 2001; 60/300,148, filedJun. 21, 2001; 60/307,063, filed Jul. 20, 2001; 60/312,563, filed Aug.15, 2001; 60/317,546, filed Sep. 5, 2001; 60/323,883, filed Sep. 20,2001; 60/334,929, filed Dec. 4, 2001; and 60/334,938, filed Dec. 4,2001, incorporated herein in their entirety by reference. Applicantsfurther incorporate herein by reference, in their entirety, thenon-provisional applications sharing these titles which were filed onDec. 12, 2001. The diamondoids that are the subject of these co-pendingapplications have not been made available for study in the past, and tothe inventors' knowledge they have never been used before in amicroelectronics application.

SUMMARY OF THE INVENTION

Embodiments of the present invention are directed toward novel uses ofdiamondoid-containing materials in the field of microelectronics.Diamondoids are bridged-ring cycloalkanes. They comprise adamantane,diamantane, and triamantane, as well as the tetramers, pentamers,hexamers, heptamers, octamers, nonamers, decamers, etc., of adamantane(tricyclo[3.3.1.1^(3,7)] decane), in which various adamantane units areface-fused to form larger structures. The compounds have a “diamondoid”topology in that their carbon atom arrangements are superimposable on afragment of an FCC diamond lattice. The present embodiments include, butare not limited to, thermally conductive films in integrated circuit(IC) packaging, low-k dielectric layers in integrated circuit multilevelinterconnects, thermally conductive adhesive films, thermally conductivefilms in (Peltier-based) thermoelectric cooling devices, passivationfilms for integrated circuit devices, dielectric layers in SRAM and DRAMcapacitors, and field emission cathodes, each application based uponincorporating one or more diamondoid-containing materials. Thediamondoid-containing materials of the present invention may befabricated as a diamondoid-containing polymer, a diamondoid-containingsintered ceramic, a diamondoid ceramic composite, a CVD diamondoid film,and a self-assembled diamondoid film. Diamondoid-containing materialsfurther include diamondoid-fullerene composites.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 schematically illustrates a process flow wherein diamondoids maybe extracted from petroleum feedstocks, processed into a useful form,and then incorporated into a specific microelectronics application;

FIGS. 2A-C illustrate exemplary polymeric materials that may befabricated from diamondoids;

FIG. 2D illustrate the variety of three-dimensional shapes availableamong the highly symmetrical 396 molecular weight hexamantanes;

FIG. 2E illustrates the variety of three-dimensional shapes availableamong enantiomers of the chiral 396 molecular weight hexamantanes;

FIGS. 2F-H illustrates the variety of carbon attachment sites on adecamantane molecule, and how attachments to different sites in apolymer may result in cross-linked materials of variable rigidity,

FIGS. 2I-K illustrate the manner in which a pentamantane may be orientedin a cross-linked polymer such that, in each case, the various diamondcrystal lattice planes are substantially parallel;

FIGS. 2L-M illustrate an exemplary chiral polymers prepared fromenantiomers of [123] tetramantane;

FIG. 2N illustrates [1(2,3)4] pentamantane.

FIG. 3A illustrates in schematic form a process flow by whichdiamondoids may be sintered into ceramic-like materials and ceramiccomposites;

FIG. 3B illustrates in schematic form a diamondoid-containing ceramicpart;

FIG. 4 illustrates an exemplary processing reactor in which adiamondoid-containing film may be synthesized using chemical vapordeposition (CVD) techniques, including the use of the diamondoidstriamantane and higher to nucleate a film grown “conventionally” byplasma CVD techniques;

FIG. 5A illustrates an exemplary diamondoid-containing film that may befabricated by self-assembly techniques;

FIG. 5B illustrates a chelate-derived linker comprising a decamantane;the linker which may comprise a linear bridging unit for connectingmolecular electronic and electro-optical devices;

FIG. 5C illustrates a chelate-derived linker comprising a nonamantane;the linker may comprise a two-dimensional bridging unit for connectingmolecular electronic and electro-optical devices;

FIGS. 6A-C illustrate an exemplary heat transfer application, in which athermally-conducting film and/or fiber facilitates heat dissipation froman integrated circuit (IC) to a conventional heat sink;

FIGS. 7A-B illustrate an exemplary heat transfer application in which adiamondoid-containing material is used as a thermally-conductive film,in this case adhering two objects together, the two objects beingmaintained at two different temperatures in a situation where rapid heatflow between the two objects is desired;

FIG. 8 illustrates an exemplary heat transfer application, in which adiamondoid-containing material is used in a thermoelectric cooler (orPeltier-based device);

FIG. 9 is a schematic a cross-section of a typical integrated circuit,in this case a complementary metal oxide semiconductor (CMOS) device,illustrating where diamondoid-containing materials may be used as low-kdielectric layers in back-end multilevel interconnection processing, andas passivation layers protecting the top surface of the IC; and

FIG. 10 illustrates schematically a cross-section of a field emissioncathode, illustrating where a diamondoid or diamondoid-containingmaterial may be used as a cold cathode filament, taking advantage of thenegative electron affinity of a diamondoid surface.

DETAILED DESCRIPTION OF THE INVENTION

According to embodiments of the present invention, diamondoids areisolated from an appropriate feedstock, and then fabricated into amaterial that is specific for a particular microelectronics application.In the following discussion diamondoids will first be defined, followedby a description of how they may be recovered from petroleum feedstocks.After recovery diamondoids may be processed into polymers, sinteredceramics, and other forms of diamondoid-containing materials, dependingon the application in which they are to be used.

Definition of Diamondoids

The term “diamondoids” refers to substituted and unsubstituted cagedcompounds of the adamantane series including adamantane, diamantane,triamantane, tetramantane, pentamantane, hexamantane, heptamantane,octamantane, nonamantane, decamantane, undecamantane, and the like,including all isomers and stereoisomers thereof. The compounds have a“diamondoid” topology, which means their carbon atom arrangement issuperimposable on a fragment of an FCC diamond lattice. Substituteddiamondoids comprise from 1 to 10 and preferably 1 to 4independently-selected alkyl substituents. Diamondoids include “lowerdiamondoids” and “higher diamondoids,” as these terms are definedherein, as well as mixtures of any combination of lower and higherdiamondoids.

The term “lower diamondoids refers to adamantane, diamantane andtriamantane and any and/or all unsubstituted and substituted derivativesof adamantane, diamantane and triamantane. These lower diamondoidcomponents show no isomers or chirality and are readily synthesized,distinguishing them from “higher diamondoids.”

The term “higher diamondoids” refers to any and/or all substituted andunsubstituted tetramantane components; to any and/or all substituted andunsubstituted pentamantane components; to any and/or all substituted andunsubstituted hexamantane components; to any and/or all substituted andunsubstituted heptamantane components; to any and/or all substituted andunsubstituted octamantane components; to any and/or all substituted andunsubstituted nonamantane components; to any and/or all substituted andunsubstituted decamantane components; to any and/or all substituted andunsubstituted undecamantane components; as well as mixtures of the aboveand isomers and stereoisomers of tetramantane, pentamantane,hexamantane, heptamantane, octamantane, nonamantane, decamantane, andundecamantane.

Adamantane chemistry has been reviewed by Fort, Jr. et al. in“Adamantane: Consequences of the Diamondoid Structure,” Chem. Rev. vol.64, pp. 277-300 (1964). Adamantane is the smallest member of thediamondoid series and may be thought of as a single cage crystallinesubunit. Diamantane contains two subunits, triamantane three,tetramantane four, and so on. While there is only one isomeric form ofadamantane, diamantane, and triamantane, there are four differentisomers of tetramantane (two of which represent an enantiomeric pair),i.e., four different possible ways of arranging the four adamantanesubunits. The number of possible isomers increases non-linearly witheach higher member of the diamondoid series, pentamantane, hexamantane,heptamantane, octamantane, nonamantane, decamantane, etc.

Adamantane, which is commercially available, has been studiedextensively. The studies have been directed toward a number of areas,such as thermodynamic stability, functionalization, and the propertiesof adamantane-containing materials. For instance, the following patentsdiscuss materials comprising adamantane subunits: U.S. Pat. No.3,457,318 teaches the preparation of polymers from alkenyl adamantanes;U.S. Pat. No. 3,832,332 teaches a polyamide polymer forms fromalkyladamantane diamine; U.S. Pat. No. 5,017,734 discusses the formationof thermally stable resins from adamantane derivatives; and U.S. Pat.No. 6,235,851 reports the synthesis and polymerization of a variety ofadamantane derivatives.

In contrast, the higher diamondoids, have received comparatively littleattention in the scientific literature. McKervay et al. have reportedthe synthesis of anti-tetramantane in low yields using a laborious,multistep process in “Synthetic Approaches to Large DiamondoidHydrocarbons,” Tetrahedron, vol. 36, pp. 971-992 (1980). To theinventor's knowledge, this is the only higher diamondoid that has beensynthesized to date. Lin et al. have suggested the existence of, but didnot isolate, tetramantane, pentamantane, and hexamantane in deeppetroleum reservoirs in light of mass spectroscopic studies, reported in“Natural Occurrence of Tetramantane (C₂₂H₂₈), Pentamantane (C₂₆H₃₂) andHexamantane (C₃₀H₃₆) in a Deep Petroleum Reservoir,” Fuel, vol. 74(10),pp. 1512-1521 (1995). The possible presence of tetramantane andpentamantane in pot material after a distillation of adiamondoid-containing feedstock has been discussed by Chen et al. inU.S. Pat. No. 5,414,189.

The four tetramantane structures are iso-tetramantane [1(2)3],anti-tetramantane [121] and two enantiomers of skew-tetramantane [123],with the bracketed nomenclature for these diamondoids in accordance witha convention established by Balaban et al. in “Systematic Classificationand Nomenclature of Diamond Hydrocarbons-I,” Tetrahedron vol. 34, pp.3599-3606 (1978). All four tetramantanes have the formula C₂₂H₂₈(molecular weight 292). There are ten possible pentamantanes, ninehaving the molecular formula C₂₆H₃₂ (molecular weight 344) and amongthese nine, there are three pairs of enantiomers represented generallyby [12(1)3], [1234], [1213] with the nine enantiomeric pentamantanesrepresented by [12(3)4], [1(2,3)4], [1212]. There also exists apentamantane [1231] represented by the molecular formula C₂₅H₃₀(molecular weight 330).

Hexamantanes exist in thirty-nine possible structures with twenty eighthaving the molecular formula C₃₀H₃₆ (molecular weight 396) and of these,six are symmetrical; ten hexamantanes have the molecular formula C₂₉H₃₄(molecular weight 382) and the remaining hexamantane [12312] has themolecular formula C₂₆H₃₀ (molecular weight 342).

Heptamantanes are postulated to exist in 160 possible structures with 85having the molecular formula C₃₄H₄₀ (molecular weight 448) and of these,seven are achiral, having no enantiomers. Of the remaining heptamantanes67 have the molecular formula C₃₃H₃₈ (molecular weight 434), six havethe molecular formula C₃₂H₃₆ (molecular weight 420) and the remainingtwo have the molecular formula C₃₀H₃₄ (molecular weight 394).

Octamantanes possess eight of the adamantane subunits and exist withfive different molecular weights. Among the octamantanes, 18 have themolecular formula C₃₄H₃₈ (molecular weight 446). Octamantanes also havethe molecular formula C₃₈H₄₄ (molecular weight 500); C₃₇H₄₂ (molecularweight 486); C₃₆H₄₀ (molecular weight 472), and C₃₃H₃₆ (molecular weight432).

Nonamantanes exist within six families of different molecular weightshaving the following molecular formulas: C₄₂H₄₈ (molecular weight 552),C₄₁H₄₆ (molecular weight 538), C₄₀H₄₄ (molecular weight 524, C₃₈H₄₂(molecular weight 498), C₃₇H₄₀ (molecular weight 484) and C₃₄H₃₆(molecular weight 444).

Decamantane exists within families of seven different molecular weights.Among the decamantanes, there is a single decamantane having themolecular formula C₃₅H₃₆ (molecular weight 456) which is structurallycompact in relation to the other decamantanes. The other decamantanefamilies have the molecular formulas: C₄₆H₅₂ (molecular weight 604);C₄₅H₅₀ (molecular weight 590); C₄₄H₄₈ (molecular weight 576); C₄₂H₄₆(molecular weight 550); C₄₁H₄₄ (molecular weight 536); and C₃₈H₄₀(molecular weight 496).

Undecamantane exists within families of eight different molecularweights. Among the undecamantanes there are two undecamantanes havingthe molecular formula C₃₉H₄₀ (molecular weight 508) which arestructurally compact in relation to the other undecamantanes. The otherundecamantane families have the molecular formulas C₄₁H₄₂ (molecularweight 534); C₄₂H₄₄ (molecular weight 548); C₄₅H₄₈ (molecular weight588); C₄₆H₅₀ (molecular weight 602); C₄₈H₅₂ (molecular weight 628);C₄₉H₅₄ (molecular weight 642); and C₅₀H₅₆ (molecular weight 656).

FIG. 1 shows a process flow illustrated in schematic form, whereindiamondoids may be extracted from petroleum feedstocks 10 in a step 11,processed into a useful form in a step 12, and then incorporated into aspecific microelectronics application shown generally at referencenumeral 13.

Isolation of Diamondoids from Petroleum Feedstocks

Feedstocks that contain recoverable amounts of higher diamondoidsinclude, for example, natural gas condensates and refinery streamsresulting from cracking, distillation, coking processes, and the like.Particularly preferred feedstocks originate from the Norphlet Formationin the Gulf of Mexico and the LeDuc Formation in Canada.

These feedstocks contain large proportions of lower diamondoids (oftenas much as about two thirds) and lower but significant amounts of higherdiamondoids (often as much as about 0.3 to 0.5 percent by weight). Theprocessing of such feedstocks to remove non-diamondoids and to separatehigher and lower diamondoids (if desired) can be carried out using, byway of example only, size separation techniques such as membranes,molecular sieves, etc., evaporation and thermal separators either undernormal or reduced pressures, extractors, electrostatic separators,crystallization, chromatography, well head separators, and the like.

A preferred separation method typically includes distillation of thefeedstock. This can remove low-boiling, non-diamondoid components. Itcan also remove or separate out lower and higher diamondoid componentshaving a boiling point less than that of the higher diamondoid(s)selected for isolation. In either instance, the lower cuts will beenriched in lower diamondoids and low boiling point non-diamondoidmaterials. Distillation can be operated to provide several cuts in thetemperature range of interest to provide the initial isolation of theidentified higher diamondoid. The cuts, which are enriched in higherdiamondoids or the diamondoid of interest, are retained and may requirefurther purification. Other methods for the removal of contaminants andfurther purification of an enriched diamondoid fraction can additionallyinclude the following nonlimiting examples: size separation techniques,evaporation either under normal or reduced pressure, sublimation,crystallization, chromatography, well head separators, flashdistillation, fixed and fluid bed reactors, reduced pressure, and thelike.

The removal of non-diamondoids may also include a pyrolysis step eitherprior or subsequent to distillation. Pyrolysis is an effective method toremove hydrocarbonaceous, non-diamondoid components from the feedstock.It is effected by heating the feedstock under vacuum conditions, or inan inert atmosphere, to a temperature of at least about 390° C., andmost preferably to a temperature in the range of about 410 to 450° C.Pyrolysis is continued for a sufficient length of time, and at asufficiently high temperature, to thermally degrade at least about 10percent by weight of the non-diamondoid components that were in the feedmaterial prior to pyrolysis. More preferably at least about 50 percentby weight, and even more preferably at least 90 percent by weight of thenon-diamondoids are thermally degraded.

While pyrolysis is preferred in one embodiment, it is not alwaysnecessary to facilitate the recovery, isolation or purification ofdiamondoids. Other separation methods may allow for the concentration ofdiamondoids to be sufficiently high given certain feedstocks such thatdirect purification methods such as chromatography including preparativegas chromatography and high performance liquid chromatography,crystallization, fractional sublimation may be used to isolatediamondoids.

Even after distillation or pyrolysis/distillation, further purificationof the material may be desired to provide selected diamondoids for usein the compositions employed in this invention. Such purificationtechniques include chromatography, crystallization, thermal diffusiontechniques, zone refining, progressive recrystallization, sizeseparation, and the like. For instance, in one process, the recoveredfeedstock is subjected to the following additional procedures: 1)gravity column chromatography using silver nitrate impregnated silicagel; 2) two-column preparative capillary gas chromatography to isolatediamondoids; 3) crystallization to provide crystals of the highlyconcentrated diamondoids.

An alternative process is to use single or multiple column liquidchromatography, including high performance liquid chromatography, toisolate the diamondoids of interest. As above, multiple columns withdifferent selectivities may be used. Further processing using thesemethods allow for more refined separations which can lead to asubstantially pure component.

Detailed methods for processing feedstocks to obtain higher diamondoidcompositions are set forth in U.S. Provisional Patent Application No.60/262,842 filed Jan. 19, 2001; U.S. Provisional Patent Application No.60/300,148 filed Jun. 21, 2001; and U.S. Provisional Patent ApplicationNo. 60/307,063 filed Jul. 20, 2001. These applications are hereinincorporated by reference in their entirety.

Materials Preparation

The term “materials preparation” as used herein refers to processes thattake the diamondoids of interest as they are isolated from feedstocks,and fabricate them into diamondoid-containing materials for use inmicroelectronic applications. These processes may include thederivatization of diamondoids, the polymerization of derivatized andunderivatized diamondoids, the sintering of diamondoid components intoceramics and ceramic composites, the use of diamondoids as a carbonprecursor in conventional CVD techniques, including the use of thediamondoids triamantane and higher to nucleate a diamond film usingconventional CVD techniques (such as thermal CVD, laser CVD,plasma-enhanced or plasma-assisted CVD, electron beam CVD, and thelike), and self-assembly techniques involving diamondoids.

Methods of forming diamondoid derivatives, and techniques forpolymerizing derivatized diamondoids, are discussed in U.S. patentapplication Serial No. 60/334,939, entitled “Polymerizable HigherDiamondoid Derivatives,” by Shenggao Liu, Jeremy E. Dahl, and Robert M.Carlson, filed Dec. 4, 2001, and incorporated herein by reference in itsentirety.

To fabricate a polymeric film containing diamondoid constituents, eitheras part of the main polymeric chain, or as side groups or branches offof the main chain, one first synthesizes a derivatized diamondoidmolecule, that is to say, a diamondoid having at least one functionalgroup substituting one of the original hydrogens. As discussed in thatapplication, there are two major reaction sequences that may be used toderivatize higher diamondoids: nucleophilic (S_(N)1-type) andelectrophilic (S_(E)2-type) substitution reactions.

S_(N)1-type reactions involve the generation of higher diamondoidcarbocations, which subsequently react with various nucleophiles. Sincetertiary (bridgehead) carbons of higher diamondoids are considerablymore reactive then secondary carbons under S_(N)1 reaction conditions,substitution at a tertiary carbon is favored.

S_(E)2-type reactions involve an electrophilic substitution of a C—Hbond via a five-coordinate carbocation intermediate. Of the two majorreaction pathways that may be used for the functionalization of higherdiamondoids, the S_(N)1-type may be more widely utilized for generatinga variety of higher diamondoid derivatives. Mono and multi-brominatedhigher diamondoids are some of the most versatile intermediates forfunctionalizing higher diamondoids. These intermediates are used in, forexample, the Koch-Haaf, Ritter, and Friedel-Crafts alkylation andarylation reactions. Although direct bromination of higher diamondoidsis favored at bridgehead (tertiary) carbons, brominated derivativesmaybe substituted at secondary carbons as well. For the latter case,when synthesis is generally desired at secondary carbons, a free radicalscheme is often employed.

Although the reaction pathways described above may be preferred in someembodiments of the present invention, many other reaction pathways maycertainly be used as well to functionalize a higher diamondoid. Thesereaction sequences may be used to produce derivatized diamondoids havinga variety of functional groups, such that the derivatives may includediamondoids that are halogenated with elements other than bromine, suchas fluorine, alkylated diamondoids, nitrated diamondoids, hydroxylateddiamondoids, carboxylated diamondoids, ethenylated diamondoids, andaminated diamondoids. See Table 2 of the co-pending application“Polymerizable Higher Diamondoid Derivatives” for a listing of exemplarysubstituents that may be attached to higher diamondoids.

Diamondoids, as well as diamondoid derivatives having substituentscapable of entering into polymerizable reactions, may be subjected tosuitable reaction conditions such that polymers are produced. Thepolymers may be homopolymers or heteropolymers, and the polymerizablediamondoid derivatives may be co-polymerized withnondiamondoid-containing monomers. Polymerization is typically carriedout using one of the following methods: free radical polymerization,cationic, or anionic polymerization, and polycondensation. Proceduresfor inducing free radical, cationic, anionic polymerizations, andpolycondensation reactions are well known in the art.

Free radical polymerization may occur spontaneously upon the absorptionof an adequate amount of heat, ultraviolet light, or high-energyradiation. Typically, however, this polymerization process is enhancedby small amounts of a free radical initiator, such as peroxides, azocompounds, Lewis acids, and organometallic reagents. Free radicalpolymerization may use either non-derivatized or derivatized higherdiamondoid monomers. As a result of the polymerization reaction acovalent bond is formed between diamondoid monomers such that thediamondoid becomes part of the main chain of the polymer. In anotherembodiment, the functional groups comprising substituents on adiamondoid may polymerize such that the diamondoids end up beingattached to the main chain as side groups. Diamondoid having more thanone functional group are capable of cross-linking polymeric chainstogether.

For cationic polymerization, a cationic catalyst may be used to promotethe reaction. Suitable catalysts are Lewis acid catalysts, such as borontrifluoride and aluminum trichloride. These polymerization reactions areusually conducted in solution at low-temperature.

In anionic polymerizations, the derivatized diamondoid monomers aretypically subjected to a strong nucleophilic agent. Such nucleophilesinclude, but are not limited to, Grignard reagents and otherorganometallic compounds. Anionic polymerizations are often facilitatedby the removal of water and oxygen from the reaction medium.

Polycondensation reactions occur when the functional group of onediamondoid couples with the functional group of another; for example, anamine group of one diamondoid reacting with a carboxylic acid group ofanother, forming an amide linkage. In other words, one diamondoid maycondense with another when the functional group of the first is asuitable nucleophile such as an alcohol, amine, or thiol group, and thefunctional group of the second is a suitable electrophile such as acarboxylic acid or epoxide group. Examples of higherdiamondoid-containing polymers that may be formed via polycondensationreactions include polyesters, polyamides, and polyethers.

Exemplary diamondoid-containing polymeric films are illustratedschematically in FIGS. 2A-2C. Referring to FIG. 2A, adiamondoid-containing polymer is shown generally at 200, where thepolymer comprises diamondoid monomers 201, 202, 203 linked throughcarbon-to-carbon covalent bonds 204. The diamondoid monomers 201, 202,203 may comprise any member of the higher diamondoid series tetramantanethrough undecamantane. The covalent linkage 204 comprises a bond betweentwo carbon atoms where each of carbon atoms of the bond are members ofthe two adjacent diamondoids. Stated another way, two diamondoids in thepolymeric chain are directly linked such that there are no interveningcarbon atoms that are not part of a diamondoid nucleus (or part of anadamantane subunit).

Alternatively, two adjacent diamondoids may be covalently linked throughcarbon atoms that are not members (part of the carbon nucleus) of eitherof the two diamondoids. Such a covalent linkage is shown schematicallyin FIG. 2A at reference numeral 205. As discussed above, adjacentdiamondoids may be covalently connected through, for example, an esterlinkages 206, an amide linkages 207, and an ether linkage is 208.

In an alternative embodiment, a diamondoid-containing polymer showngenerally at 220 in FIG. 2B comprises a copolymer formed from themonomers ethylene and a higher diamondoid having at least one ethylenesubstituent. The diamondoid monomer shown at 221 contains onesubstituent ethylene group. The diamondoid monomer shown at 222 containstwo ethylene substituents, and could have more than two substituents.Either or both of these diamondoids may be copolymerized with ethylene223 itself, as a third monomer participating in the reaction, to formthe co-polymer 220 or subunits thereof Because the diamondoid monomer222 has two substituent polymerizable moieties attached to it, thisparticular monomer is capable of cross-linking chains 224 and chain 225together. Such a cross-linking reaction is capable of producing polymershaving properties other than those of the polymer depicted in FIG. 2A,since for the FIG. 2A polymer the diamondoid nuclei are positionedwithin the main chain. A consequence of the structures formed in FIGS.2A and 2B is that it is possible to incorporate metallic elements,particles, and inclusions (illustrated as M1 to M3) by inserting theminto the interstities of folded and cross-linked polymeric chains.Diamondoid-containing materials may be doped in such a manner withalkali metals, alkali earth metals, halogens, rare earth elements, B,Al, Ga, In, Ti, V, Nb, and Ta to improve thermal conductivity ifdesired. The relative ratios of the monofunctional diamondoid monomer,the difunctional diamondoid monomer, and the ethylene monomer in theexemplary polymer of FIG. 2B may of course be adjusted to produce thedesired properties with regard to stiffness, compactness, and ease ofprocessing.

The exemplary polyimide-diamondoid polymer shown generally at 230 inFIG. 2C contains segments of polyimide chains derived fromrepresentative groups selected to illustrate certain relationshipsbetween structure and properties, in particular, how the properties ofthe exemplary polymer relate to the processing it has undergone. Thedianhydride PMDA (pyromellitic dianhydride) shown at 231 and the diaminediaminofluorenone 232 are introduced into the chain for rigidity. Thedianhydride BTDA (benzophenonetetracarboxylic dianhydride) shown at 233provides the capability of further reaction at the carboxyl site,possibly for crosslinking purposes, and/or for the potential inclusionof metallic moieties into the material. The dianhydride oxydiphthalicdianhydride (ODPA) shown at 234, and the diamines oxydianiline (ODA) at235 and bisaminophenoxybenzene at 236 may be introduced for chainflexibility and ease of processing of the material. Additionally,fluorinated dianhydrides such as 6FDA (not shown) may be introduced tolower the overall dielectric constant of the material.

The diamondoid components of the exemplary polymer illustratedschematically in FIG. 2C comprise a pentamantane diamondoid at 266,which is positioned in the main chain of the polymer, and an octamantanediamondoid at 237, which comprises a side group of thediamondoid-polyimide polymer at a position of a diamine (in thisexemplary case, diaminobenzophenone) component. A diamondoid component238 may be used as a cross-linking agent to connect two adjacent chains,through covalent linkages, or diamondoid component 238 may be passivelypresent as an unfunctionalized “space filler” wherein it serves toseparate main polymeric chains simply by steric hindrance. Folding ofthe main polymeric chains, particularly when diamondoid “fillers” 238are present, may create voids 239, which may serve to reduce the overalldielectric constant of the material, since the dielectric constant ofair (if it is the gas within the void), is one.

The diamond nanocrystallites (higher diamondoids) that may beincorporated into a diamondoid-containing material in general, and intopolymeric materials in particular, have a variety of well-definedmolecular structures, and thus they may be attached to each other,attached to a main polymer chain, used as cross-linking agents, etc., ina great variety of ways. The six hexamantanes illustrated in FIG. 2D areexamples of a higher diamondoid having a highly symmetrical shape, andthe 12 chiral hexamantanes illustrated in FIG. 2E are examples ofenantiomeric pairs.

The molecular sites and the geometries of the attachments of a higherdiamondoid to another diamondoid, and to a polymer chain, will alsoaffect the properties of resulting materials. For example, theinterconnection of higher diamondoid units through tertiary“bridge-head” carbons, as illustrated in FIG. 2F, will result instronger, more rigid materials than those which result frominterconnection through secondary carbons, as in FIG. 2G. Furthermore,attachment through tertiary carbons that are themselves bonded to thehighest number of quaternary carbons in a higher diamondoid(nanocrystallite) will provide the strongest, most rigid materials, asin FIG. 2H.

There are other properties of higher diamondoids that may be exploitedto design new materials with desirable properties. Higher diamondoidsdisplay classical diamond crystal faces such as the (111), (110), and(100) planes, as shown in FIGS. 2I, 2J, and 2K for the diamondoid[1(2,3)4] pentamantane illustrated in FIG. 2N. These higher diamondoidsmay be oriented in materials such as polymers so that the resultingdiamond nanocrystallites may have co-planer diamond faces. Thediamondoids with chiral structure, may be used to fabricate theexemplary chiral polymers illustrated in FIGS. 2L, 2M. These kinds ofchiral polymers have potential uses in photonics, and for theintegration of photonic and electronic devices.

The diamondoid-containing polymers discussed above may be applied to asubstrate undergoing microelectronic processing by any of methods knownin the art, such as spin coating, molding, extrusion, and vapor phasedeposition.

The weight of diamondoids and substituted diamondoids as a function ofthe total weight of the polymer (where the weight of the diamondoidfunctional groups are included in the diamondoid portion) may in oneembodiment range from about 1 to 100 percent by weight. In anotherembodiment, the content of diamondoids and substituted diamondoids isabout 10 to 100 percent by weight. In another embodiment, the proportionof diamondoids and substituted diamondoids in the polymer is about 25 to100 percent by weight of the total weight of the polymer.

Another technique that may be used to form isolated diamondoids intouseful and application-specific shapes is sintering, using processesthat typically are used in the ceramics industry. Ceramics have beendefined by M. Barsoum in Fundamentals of Ceramics (McGraw Hill, NewYork, 1997), pp. 2-3. In general, ceramics may be defined as solidsformed by heating (often under pressure) mixtures of metals, nonmetallicelements such as nitrogen, oxygen, hydrogen, fluorine, and chlorine, and“nonmetallic elemental solids” including carbon, boron, phosphorus, andsulfur. Ceramics have varying degrees of ionic and covalent bonding.Many of the hardest, most refractory, and toughest ceramics arestructures in which covalent bonding predominates. Examples of covalentceramics are boron nitride (BN), silicon carbide (SiC), boron carbide(B₄C), silicon nitride (Si₃N₄). Although un-derivatized diamondoids willmost likely form van der Waals solids with a certain cohesive energyexerted between adjacent surface carbons and their attached hydrogens,diamondoids may be derivatized as discussed above such that they possessfunctionality on their surfaces capable of interacting both ionically,and covalently, with other ceramic materials. Such solids may be thoughtof as behaving in general like a ceramic, but having small, diamond-likeparticulate inclusions.

A process flow for generating the diamondoid-containing ceramic and/orceramic composite is shown generally in FIG. 3A. Shown at referencenumeral 301 is the isolation of diamondoids from feedstocks. Theisolated diamondoids may then be derivatized with the desired functionalgroups as discussed above, as shown at 302. However, in someembodiments, it may not be necessary to derivatize the diamondoids. At303, the diamondoids (which may or may not be derivatized) may be mixedwith a nondiamondoid powder, the latter which may comprise any otherceramic materials known in the art. An exemplary list of such ceramicsis given by Chiang et al. in “Physical Ceramics,” Table 1.3 (Wiley, NewYork, 1997), incorporated herein in entirety by reference. It will beapparent to one skilled in the art that a substituent may be attached tothe diamondoid, the substituent belonging to Group IA or Group IIA ofthe periodic table such that the the substituent will be an electrondonor. Such elements are useful if a high degree of ionic character isdesired. Examples of such elements include Li, Be, Na, Mg, K, Ca, andSr. Alternatively, powders containing metal particles 305 from GroupsIIIB to IIB may be mixed with the diamondoid materials including alloysof such metals. Noble metals such as Au, Ag, Pa, Pt and their alloys maybe desirable since these materials are less susceptible to oxidation.Non-noble metals such as Cu, Ni, Fe, Co, Mo, W, V, Zn, and Ti, and theiralloys, may also be used. Low melting point metals such as Sn, Al, Sb,In, Bi, Pb, and their alloys, or conventional low melting point soldersmay be mixed with the diamondoids, as well as semiconducting materialssuch as Si and Ge. The diamondoids may also be mixed with organometalliccompounds to convey a desired degree of electrical conductivity to theresulting ceramic, and these organometallic compounds may reactcovalently with functional groups on the diamondoids.

The mixing of the functionalized and/or non-functionalized diamondoidswith ceramic and/or metal powders is performed by way of example as adry process, such as stirring or ball milling, or as a wet processforming a powder mixed slurry incorporating a liquid capable of beingevaporated (such as alcohol, acetone, and water), optionally with theaddition of a binder to improve the adhesion of the constituentparticles to one another.

The mixture may then be sintered at elevated pressure and temperature,according to processes well known in the art, to yield a ceramic solidand/or ceramic composite. It may be preferable to machine the sinteredproduct into a specific shape at 308, or the sintering product at 307may be formed in a mold such that the sintered product has the desiredshape. Prior to sintering, the mixture 306 may be pressed into a greenshape 309 although this step is optional. The pressing step 309 isadvantageous in some instances in that it may eliminate the trapping ofgases, although it will be noted by one skilled in the art that in someapplications a porosity is desired. The pressing step 309 may also allowsoft metals, such as solders, if present, to flow within the system. Insome embodiments, the pressing step 309 may be performed in conjunctionwith a vacuum applied to any or all of the mixture to facilitate shapingof the solid, or to remove undesired gaseous byproducts.

One such exemplary sintered diamondoid-containing ceramic and/or ceramiccomposite is illustrated schematically in FIG. 3B. The sintereddiamondoid-containing ceramic is shown generally at 320, wherediamondoid particles 321, 322, and 323 are shown. The diamondoidparticle at 321 may be derivatized such that it is bound in the ceramicmaterial by chemical bonds, or the diamondoids may be underivatized andbound in the material substantially by mechanical forces. In analternative embodiment, the diamondoid particles and/or diamondoidaggregates at 322 and 323 may contain functional groups 324 and 325,respectively, to facilitate adhesion of the diamondoid particles toceramic particles 326. Alternatively, a binder 327 may be present tofacilitate adhesion of diamondoid particles 322 and 323 to ceramicparticles 326, in some cases by forming covalent bonds throughfunctional groups 324 and 325. Large metallic inclusions 328 may bepresent to facilitate electrical conduction.

The ceramic shown generally at 320 may be processed into specific shapesand forms, having for example protrusions 330 for nesting andpositioning the ceramic in place, or regions 331 that may have specificactive functions. The shaping step 308 (see again FIG. 3A) may beaccomplished by any of the techniques known in the art, such as forging,machining, grinding, or stamping.

The weight of diamondoids and substituted diamondoids as a function ofthe total weight of the ceramic (where the weight of the diamondoidfunctional groups are included in the diamondoid portion) may in oneembodiment range from about 1 to 99.9 percent by weight. In anotherembodiment, the content of diamondoids and substituted diamondoids isabout 10 to 99 percent by weight. In another embodiment, the proportionof diamondoids and substituted diamondoids in the ceramic is about 25 to95 percent by weight of the total weight of the ceramic.

Thus far, the present description has focused on polymerization andceramic sintering as techniques for forming diamondoids into applicationspecific forms. Two additional techniques, chemical vapor deposition(CVD) and self-assembly, will be discussed next. For instance,conventional methods of synthesizing diamond by plamsa enhanced chemicalvapor deposition (PECVD) techniques are well known in the art, and dateback to around the early 1980's. Although it is not necessary to discussthe specifics of these methods as they relate to the present invention,one point in particular that should be made since it is relevant to therole hydrogen plays in the synthesis of diamond by “conventional”plasma-CVD techniques.

In one method of synthesizing diamond films discussed by A. Erdemir etal. in “Tribology of Diamond, Diamond-Like Carbon, and Related Films,”in Modern Tribology Handbook, Vol. Two, B. Bhushan, Ed. (CRC Press, BocaRaton, 2001) pp. 871-908, a modified microwave CVD reactor is used todeposit a nanocrystalline diamond film using a C₆₀ fullerene, ormethane, gas carbon precursor. This method differs from conventional CVDtechniques in that the deposition was conducted in the absence ofhydrogen, with argon used instead. Methane/argon gas mixtures are beingincreasingly used when nanocrystalline diamond films are desired, asdiscussed above. To introduce the C₆₀ fullerene precursor into thereactor, a device called a “quartz transpirator” is attached to thereactor, wherein this device essentially heats a fullerene-rich soot totemperatures between about 550 and 600° C. to sublime the C₆₀ fullereneinto the gas phase.

It is contemplated that a similar device may be used to sublimediamondoids into the gas phase such that they to may be introduced to aCVD reactor. An exemplary reactor is shown in generally at 400 in FIG.4. A reactor 400 comprises reactor walls 401 enclosing a process space402. A gas inlet tube 403 is used to introduce process gas into theprocess space 402, the process gas comprising methane, hydrogen, andoptionally an inert gas such as argon. A diamondoid subliming orvolatilizing device 404, similar to the quartz transpirator discussedabove, may be used to volatilize and inject a diamondoid containing gasinto the reactor 400. The volatilizer 404 may include a means forintroducing a carrier gas such as hydrogen, nitrogen, argon, or an inertgas such as a noble gas other than argon, and it may contain othercarbon precursor gases such as methane, ethane, or ethylene.

Consistent with conventional CVD reactors, the reactor 400 may haveexhaust outlets 405 for removing process gases from the process space402; an energy source for coupling energy into process space 402 (andstriking a plasma from) process gases contained within process space402; a filament 407 for converting molecular hydrogen to monoatomichydrogen; a susceptor 408 onto which a diamondoid containing film 409 isgrown; a means 410 for rotating the susceptor 408 for enhancing thesp³-hybridized uniformity of the diamondoid-containing film 409; and acontrol system 411 for regulating and controlling the flow of gasesthrough inlet 403, the amount of power coupled from source 406 into theprocessing space 402; and the amount of diamondoids injected into theprocessing space 402 the amount of process gases exhausted throughexhaust ports 405; the atomization of hydrogen from filament 407; andthe means 410 for rotating the susceptor 408. In an exemplaryembodiment, the plasma energy source 406 comprises an induction coilsuch that power is coupled into process gases within processing space402 to create a plasma 412.

A diamondoid precursor (which may be a triamantane or higher diamondoid)may be injected into reactor 400 according to embodiments of the presentinvention through the volatilizer 404, which serves to volatilize thediamondoids. A carrier gas such as methane or argon may be used tofacilitate transfer of the diamondoids entrained in the carrier gas intothe process space 402. The injection of such diamondoids may facilitategrowth of a CVD grown diamond film 409 by allowing carbon atoms to bedeposited at a rate of about 10 to 100 or more at a time, unlikeconventional plasma CVD diamond techniques in which carbons are added tothe growing film one atom at a time. Growth rates may be increased by atleast two to three times and in some embodiments, growth rates may beincreased by at least an order of magnitude.

It may be necessary, in some embodiments, for the injected methaneand/or hydrogen gases to “fill in” diamond material between diamondoids,and/or “repair” regions of material that are “trapped” between theaggregates of diamondoids on the surface of the growing film 409.Hydrogen participates in the synthesis of diamond by PECVD techniques bystabilizing the sp³ bond character of the growing diamond surface. Asdiscussed in the reference cited above, A. Erdemir et al. teach thathydrogen also controls the size of the initial nuclei, dissolution ofcarbon and generation of condensable carbon radicals in the gas phase,abstraction of hydrogen from hydrocarbons attached to the surface of thegrowing diamond film, production of vacant sites where sp³ bonded carbonprecursors may be inserted. Hydrogen etches most of the double or sp²bonded carbon from the surface of the growing diamond film, and thushinders the formation of graphitic and/or amorphous carbon. Hydrogenalso etches away smaller diamond grains and suppresses nucleation.Consequently, CVD grown diamond films with sufficient hydrogen presentleads to diamond coatings having primarily large grains with highlyfaceted surfaces. Such films may exhibit the surface roughness of about10 percent of the film thickness. In the present embodiment, it may notbe as necessary to stabilize the surface of the film, since carbons onthe exterior of a deposited diamondoid are already sp³ stabilized.

Diamondoids may act as carbon precursors for a CVD diamond film, meaningthat each of the carbons of the diamondoids injected into processingspace 402 are added to the diamond film in a substantially intact form.In addition to this role, diamondoids 413 injected into the reactor 400from the volatilizer 404 may serve merely to nucleate a CVD diamond filmgrown according to conventional techniques. In such a case, thediamondoids 413 are entrained in a carrier gas, the latter which maycomprise methane, hydrogen, and/or argon, and injected into the reactor400 at the beginning of a deposition process to nucleate a diamond filmthat will grow from methane as a carbon precursor (and not diamondoid)in subsequent steps. In some embodiments, the selection of theparticular isomer of a particular diamondoid may facilitate the growthof a diamond film having a desired crystalline orientation that may havebeen difficult to achieve under conventional circumstances.Alternatively, the introduction of a diamondoid nucleating agent intoreactor 400 from volatilizer 404 may be used to facilitate anultracrystalline morphology into the growing film for the purposesdiscussed above.

As described by D. M. Gruen in “Nucleation of ultrananocrystallinediamond films” in Properties, Growth, and Applications of Diamond;edited by M. H. Nazaré and A. J. Neves (Inspec, Exeter, 2001), pp.303-306, in order to obtain ultrananocrystalline film growth having amicrostructure consisting of a 3-5 nanometer crystallite size, thenucleation rate has to increase from a conventional value of 10⁴ cm⁻²s⁻¹ to about 10¹⁰ cm⁻² s⁻¹. This 10⁶ order of magnitude increase innucleation rate may be provided by the introduction of sublimeddiamondoids into the reactor 400 at the beginning of a CVD depositionprocess.

It has been pointed out by W. Kulisch in “Deposition of Diamond-LikeSuperhard Materials,” Section 4.2, Nucleation of Diamond (Springer,Berlin, 1999), that the nucleation of diamond is complicated by the factthat one must distinguish between carbide-forming substrates (e.g. Siand Mo) and non-carbide forming substrates (Ni and Pt). In the formercase, the diffusion of carbon into the substrate leads to a carbidelayer which acts as a barrier to further carbon diffusion, and anincreased carbon concentration on the surface. The barrier is anecessary but not sufficient condition for the rapid formation of nucleion the surface of the substrate. For non-carbide forming substrates, onthe other hand, deposition begins with the formation of a graphitic, andgenerally greater carbon-like layer before any diamond nuclei can beobserved. According to embodiments of the present invention, theinjection of diamondoid containing gases into reactor 400 at thebeginning of a CVD diamond process may render the reaction independentof the nature of the substrate, since the diamondoid particles acting asnuclei are so large and thermodynamically stable that diffusion ofcarbon into the substrate is not practical. In one embodiment, a methodof nucleating the growth of a diamond film involves the injection of atriamantane diamondoid into the CVD reactor at the beginning of adeposition process. In another embodiment, diamondoid film growth isnucleated with a higher diamondoid, where the higher diamondoid maycomprise tetramantane, pentamantane, hexamantane, heptamantane,octamantane, nonamantane, decamantane, and undecamantane, includingcombinations thereof and combinations with triamantane. Of course, thediamondoids mentioned above may be used to nucleate diamond films grownby other types of processes in other types of reactors, and theseembodiments are not limited to chemical vapor deposition.

The weight of diamondoids and substituted diamondoids, as a function ofthe total weight of the CVD film (where the weight of the diamondoidfunctional groups are included in the diamondoid portion), may in oneembodiment range from about 1 to 99.9 percent by weight. In anotherembodiment, the content of diamondoids and substituted diamondoids isabout 10 to 99 percent by weight. In another embodiment, the proportionof diamondoids and substituted diamondoids in the CVD film relative tothe total weight of the film is about 25 to 95 percent by weight.

In addition to techniques where diamondoids are used as precursors forCVD diamond film deposition and nucleation entities, diamondoids mayalso be incorporated into a film by self-assembly techniques.Diamondoids and their derivatives can undergo self-assembly in a varietyof ways. For example, diamondoid-thiols may self-assemble on variousmetal surfaces, as illustrated generally in FIG. 5A, where a diamondoidmonolayer 501 has self-assembled on a metal layer 502. The diamondoidscomprising the monolayer 501 may be either lower diamondoids, higherdiamondoids, or both. If the diamondoids of the monolayer 501 are lowerdiamondoids, they may be synthesized or isolated from a suitablefeedstock. If the diamondoids comprising monolayer 501 are higherdiamondoids, they may be isolated from a suitable feedstock whensynthesis is not possible. These selected diamondoids can then bederivatized, in this example, to form a thiol-diamondoid 503. Thethio-diamondoid derivative 503 can then self-assemble, and undergopartial or complete orientation in the process, by bonding to the metalsurface 502. In one embodiment, the metal surface 502 comprises gold ora gold alloy. Alternatively, the diamondoid layer 501 may self-assembleon the metal layer 502 through alkyl sulfide groups, an example of whichmay be represented by the sequence “metal layer502-S—C₁₂H₂₄-diamondoid,” or “metal layer 502-S—R-diamondoid,” where Rrepresents an alkyl group.

In an alternative embodiment, a diamondoid layer may self-assemble byhydrogen bonding to either a substrate or to some other layer, includinganother diamondoid-containing layer, or a non-diamondoid containinglayer. In the exemplary embodiment illustrated in FIG. 5A, thediamondoid layer 501 has hydrogen-bonded to a non-diamondoid layer 504,such that the diamondoid layer 501 is sandwiched between thenon-diamondoid layer 504 and the metal layer 502. It will be apparent tothose skilled in the art that the hydrogen-bonding of the diamondoidlayer 501 to the non-diamondoid layer 504 does not require thederivatization of the diamondoid layer 501 if hydrogens 505 on thediamondoid layer 501 are bonding to hydroxyl groups 506 on thenon-diamondoid layer 504. Hydrogen bonding could occur, however, betweenhydroxyl groups on the diamondoids 503 and hydrogens on thenon-diamondoid layer 504, in which case the diamondoids 503 might bederivatized.

In addition to a chemically based self-assembly, a diamondoid ordiamondoid-containing layer could self-assemble through electrostaticinteractions. This possibility is illustrated at the top of FIG. 5A,where a diamondoid layer 507 has electrostatically self-aligned on thenon-diamondoid layer 504 through electrostatic interactions 508. In thisexample the diamondoid layer 507 has positive charges and the substrateon which it is aligning has negative charges, but of course this couldbe reversed, and there could be a mixture of positive and negativecharges on each layer.

In addition to the examples cited above, a derivatized diamondoid mayself-assemble on a layer having a plurality of functional groups thatare complimentary to the derivatizing groups on the diamondoids.Likewise, derivatized diamondoids may polymerize in a self-assemblyingfashion given the complementary nature of functional groups. In otherwords, monomers may be induced to self-assemble into polymers. Theformation of polymers, like the self-assembling chemical reactionsdescribed above, is a method of locking diamondoids into desiredorientations with desired thicknesses. The polymers can be synthesizeddirectly on a desired substrate.

Formation of molecular crystals is another means of inducing diamondoidsand their derivatives to self-assemble. Once a particular diamondoid hasbeen isolated and purified (and derivatized if desired), crystals can begrown by slowly evaporating diamondoid solvents such as cyclohexane. Byvarying conditions such as the temperature, the solvent composition andthe speed of solvent evaporation, the size of the individual crystalscan be controlled. They can range in size from nanometers tocentimeters, depending on the processing conditions. The resultingself-assembled crystals can orient the diamondoid molecules in apreferred direction or set of directions. Self-assembled crystals may begrown directly on a desired substrate.

Higher diamondoid derivatives containing two or more chelation sites canbe used to construct nanometer-sized linker units that self-assemble inthe presence of appropriate metal ions to form long chains ofalternating metal ion and linker subunits. An example is shown in FIG.5B, in which [1231241(2)3] decamantane functions as a linear linkerunit. In FIG. 5C, [121(2)32(1)3] nonamantane functions as a2-dimensional linker unit. Linear linkers using only adamantane havebeen described by J. W. Steed et al. in “Supermolecular Chemistry,”(Wiley, New York, 2001), pp. 581-583. Various three-dimensionalself-assembling units are possible given the wide range of higherdiamondoid structures. Additionally, this approach may be used to designlinker units which self-assemble into desired, predetermined arrays.

The weight of diamondoids and substituted diamondoids that may beincorporated into a self-assembled film, as a function of the totalweight of the film (where the weight of the functional groups areincluded in the diamondoid portion) may in one embodiment range fromabout 1 to 99.99 percent by weight. In another embodiment, the contentof diamondoids and substituted diamondoids is about 10 to 98 percent byweight. In another embodiment, the proportion of diamondoids andsubstituted diamondoids in the ceramic is about 25 to 98 percent byweight of the total weight of the self-assembled film.

Applications of Diamondoid-containing Materials to Microelectronics

These applications include microelectronics packaging, passivation filmsfor integrated circuit devices (ICs), low-k dielectric layers inmultilevel interconnects, thermally conductive films, including adhesivefilms, thermoelectric cooling devices, and field emission cathodes.

The process of preparing an integrated circuit (IC) chip for use iscalled packaging. An overview of IC packaging has been presented by T.Tachikawa in a chapter entitled “Assembly and Packaging,” ULSITechnology (McGraw Hill, New York, 1996), pp. 530-586. The purpose of ICpackaging is to provide electrical connections for the chip, mechanicalenvironmental protection, as well as a conduit for dissipating heat thatevolves as the chip is operated. Integrated circuit devices includememory, logic, and microprocessing devices. Packaging devices includehermetic-ceramic and plastic packages. Each have their own level ofpower dissipation, and pose their own requirements in terms of thethermal path to dissipate heat. Integrated circuit clock speeds andpower densities are increasing, and since package sizes aresimultaneously decreasing, thermal dissipation becomes a long-termpackaging reliability issue. The heat generated by an IC is proportionalto its computing power, which is the product of the number oftransistors in the IC and their clock frequencies. Although thecomputing power of a typical IC has increased significantly in recentyears, design rules such as the operating temperature have notsubstantially changed, placing demands on the methods by whichdissipated heat is removed.

As discussed by T. Tachikawa, chip interconnection typically consists oftwo steps. In a first step, the back of the chip is mechanically bondedto an appropriate medium, such as a ceramic substrate or the paddle of ametal lead frame. Chip bonding provides, among other things, a thermalpath for heat to be dissipated from the chip to the substrate medium. Ina second step, the bond pads on the circuit side of the chip areelectrically connected to the package by wire bonding, typically usingfine metal wires of gold or aluminum.

As the amount of heat generated by the integrated circuit increases, sotoo does the junction temperature of the components transistors in aproportional manner. The failure rate of the semiconducting device is ingeneral related to the junction temperature at which the device isoperated. It is generally known to provide a heat spreader or heat sinkin order to transfer the heat generated by the device away from thedevice and into either the surrounding air or the substrate, thusreducing transistor junction temperatures. Heat sinks are typicallyconstructed from materials having high thermal conductivity, such ascopper, aluminum, BeO, and diamond, although other material propertiesare taken into consideration, such as density, and thermal expansioncoefficient. Since CVD diamond has a thermal conductivity (up to 2500W/mK) three to five times greater than that of copper (about 391 W/mK) athermal expansion coefficient similar to that the Si and GaAs, and highelectrical resistivity, CVD diamond offers an attractive alternative totraditional metallic heat spreading materials, particularly when formedsuch that they facilitate transfer of heat from an integrated circuit toa conventional metallic heat sink/substrate.

An exemplary model of a packaged integrated chip is shown generally at600 in FIG. 6A to illustrate the processes by which heat is dissipatedfrom an integrated circuit, where a chip 601 is supported by a frame(not shown) within a plastic package 602. Metallic bond wires 604A, 604Bconnect the chip to a lead 605A, 605B, respectively. Dissipated heat isconducted away from the chip by conductive heat transfer along pathways606 (according to Fourier's equation), by convection 607 (Newton'scooling law), and by radiation 608 (following the Stefan-Boltzmann law).

In one embodiment of the present invention, a diamondoid containing heattransfer film 620 is positioned adjacent to integrated circuit chip 601and a heat sink 610 positioned inside the package 625. By providing heattransfer film 620, heat from the integrated circuit 601 may diffusealong a pathway 621 in a substantially direct route into the heat sinkmaterial 610, or alternatively, may be conducted along heat transferpath 622 into the heat sink at 623. This provides an additional pathwayfor the removal of heat. By providing heat transfer film 620, andpathway 622, heat may be dispersed into heat sink 610 at positions 623that are laterally displaced from the integrated circuit chip 601, andin this manner, heat removal from integrated circuit 601 is facilitated.

In another embodiment of the present invention, there may not besufficient room within or immediately adjacent to the integrated circuitchip 601 for a heat sink. In FIG. 6C, a larger heat sink 630 ispositioned outside the package 635. In this embodiment, heat pipes orheat conduits 631, 632 may be used to conduct heat away from the chip toa heat sink located remotely from the package. The heat conduits may bein fiber form, and may be inserted into the integrated circuit chipitself at locations 633, 634, or they may communicate with thermal vias(not shown) within the chip. The heat conducting conduits may beflexible fibers, or rigid rods. There may be from about 1 to 100 of theheat conducting fibers or rods.

The heat transfer film 620 of FIG. 6B, and heat conduits 630 of FIG. 6Cmay comprise any of the diamondoid-containing materials discussed above,such as a polymerized diamondoid film, a diamondoid-containing ceramicand/or ceramic composite, a CVD deposited diamondoid-containing film, aCVD diamond film nucleated by diamondoids, or a diamondoid-containingfilm deposited by self-assembly techniques. According to one embodimentof the present invention, the heat transfer film 620 comprises adiamondoid-containing polymer similar to that depicted in FIG. 2A,particularly where diamondoid 201 is connected to an adjacent diamondoid202 through either covalent linkage 204 or covalent linkage 205. Thecovalent linkage 204 bonds carbons that are members of the diamondoidnucleus itself; alternatively, the covalent linkage 205 is a bond inwhich the constituent carbons of the bond comprise attachments orsubstituents to the diamondoid nuclei they are connecting.

It will be recognized by those skills in the art that since diamondoidsthemselves are hydrocarbons, heat transfer within a van der Waals solidwill be less efficient than through a polymer having a continuousnetwork of C—C bonds. The heat transfer film 620 may be very thin,comprising a minor layer of diamondoids such that the heat flow isthrough just the diameter of a single diamondoid. In this manner, asabove, a continuous network of C—C bonds is provided.

Diamondoids may be used as thermally-conducting films in othermicroelectronics applications, such as an adhesive film, or as anintermediate heat transfer film as part of a thermoelectric coolingdevice. An exemplary application of a thermally conducting adhesive filmis shown generally with device 700 in FIGS. 7A-B. The device 700 in FIG.7A comprises an object 701 at a temperature T₁ adhesively connected toan object 702 at temperature T₂, the connection means comprising athermally-conducting adhesive film 703. In this example, it is desiredto adhere the object 701 to the object 702, with a minimum of resistanceof heat flow between the two bodies. At one time, the temperature T₁ maybe for example greater than the temperature T₂, and in this case, heatwill be allowed to flow flow rapidly from the object 701 to the object702, an interaction 704, with a minimum of thermal resistance.

As this exemplary device 700 is being operated, the temperatures of thetwo bodies may change virtually instantaneously, such that at a latertime the temperature of the body 702 is T₄ and the temperature of thebody 701 is T₃, where T₄ is greater than T₃. As the device is beingoperated into the second configuration of FIG. 7B, it may still bedesirable to adhere to the object 701 to the body 702 with asubstantially minimal resistance to heat flow. In this case, thethermally conducting films 703 allows heat to flow in an reversedirection 705, from the object 702 back to the object 701.

The thermally-conducting adhesive film 703 may comprise any of thematerial forms discussed above, such as as a polymerized diamondoidfilm, a diamondoid-containing ceramic and/or ceramic composite, a CVDdeposited diamondoid-containing film, a CVD diamond film nucleated bydiamondoids, or a diamondoid-containing film deposited by self-assemblytechniques. In a preferred embodiment, however, the thermally-conductingadhesive film 703 is a diamondoid-containing polymeric film, in whichsubstituent groups are attached either to the diamondoid nucleithemselves, or to other portions of the polymer, such that adhesion isfacilitated. An exemplary functional group that may be incorporated intoa diamondoid-containing film to facilitate adhesion is a carboxyl group.Such a device configuration is contemplated to be useful in a variety ofapplications in microelectronics and nanotechnology. Of course, it willbe appreciated by those skilled in the art that the surface 706 of body701 and surface 707 of body 702, in other words, the two surfaces being“glued” together, do not have to comprise smooth surfaces 706, 707, andin some embodiments of the present invention, a flexiblediamondoid-containing adhesive film is well-suited to adhereirregularly-shaped materials one to another, such as the rough surfacesdepicted at 708, 709.

An additional exemplary use of a diamondoid-containing material havingthermally conductive and electrically insulating properties is athermoelectric cooling device. It is known in the art that CMOS logicdevices operate significantly faster at low temperatures. Efforts havebeen made in the past to reduce the temperature at which amicroelectronic device is operated, including methods that includethermoelectric devices.

An exemplary microelectronics application in which a film that is boththermally conducting and electrically insulating may be useful is thethermoelectric device shown generally at 800 in FIG. 8. Thethermoelectric device 800 has an element 801 whose purpose is to pumpheat from a cold substrate 802 to a hot substrate 803. Thethermoelectric element 801 operates in a conventional manner bysupplying DC power from a supply 804 to provide a potential differenceacross the junction of two dissimilar materials, which may besemiconductors. In FIG. 8, the potential is applied between points 805and 806. The temperature of substrate 803 is at a high temperature, forexample, T_(high), whereas the temperature of substrate 802 is at alow-temperature, for example, T_(low). The purpose of the thermoelectricdevice 801 is to remove heat from the substrate at the low-temperature802 in a thermally “uphill” manner to substrate 803.

The thermal conductivity of the thermoelectric device 800 depends inpart upon the characteristics of the element 801, as well as the thermalconductivites of substrates 802 and 803. Any resistance to the transferof heat from substrate 802 to substrate 803 reduces the efficiency atwhich the device 800 operates. According to one embodiment of thepresent invention, the efficiency of the device 800 may be enhanced byproviding a thermally conducting layer 802A adjacent to a heat sinklayer 802B. Likewise, the substrate 803 may comprise a thermallyconducting layer 803A positioned adjacent to a heat sink layer 803B. Theenhanced level of thermal conductivity of the layers 802A and 803Areduces the thermal resistance for removing heat from the system via thesubstrates 802 and 803, respectively. In an embodiment of the presentinvention, the thermally-conducting layers 802A and 803A may compriseany of the material discussed above, such as as a polymerized diamondoidfilm, a diamondoid-containing ceramic and/or ceramic composite, a CVDdeposited diamondoid-containing film, a CVD diamond film nucleated bydiamondoids, or a diamondoid-containing film deposited by self-assemblytechniques. In a preferred embodiment, however, the thermally-conductinglayers 802A and 803A comprise a diamondoid-containing polymer film or adiamondoid-containing ceramic.

Referring again to FIG. 8, thermally conducting layers 802A and 803A areelectrically insulating as well in order to provide electrical isolationof the thermoelectric device 800. It will be obvious to those skilled inthe art that if the layers 802A and 803A are not sufficientlyelectrically insulating, then the potential difference across element801 attempted by the supply 804 may be less than not desired, as well asunreliable or nonuniform. The electrical insulation and thermalconduction properties of diamondoid films suggest a utility inmicroelectronic applications such as thermoelectric device 800 whereboth properties are simultaneously desired.

In one embodiment of the present invention, the thermal conductivity ofthe material used in the above mentioned applications is at least 200W/m K. In a preferred embodiment of the invention, the thermalconductivity of the material is at least 500 W/m K. In an even morepreferred embodiment of the present invention, the thermal conductivityof the material is at least 1,000 W/m K.

An example of an application in which electrical insulation of adiamondoid-containing material is the property of greatest interestrelates to so-called back-end processing of an integrated circuitdevice. As transistor sizes in ultra large-scale integrated circuits aredecreased, it is desirable to reduce the capacitance of the metalinterconnection lines to each other to minimize the delays of electricalsignals conducted by the metal interconnection lines, as well as toreduce “crosstalk” between the lines. This permits the integratedcircuit to maintain or possibly even increase clock speed as the size ofthe component transistors are reduced.

One method for reducing the capacitance between interconnection lines isto deposit a polymeric or other insulating material on the integratedcircuit chip between the metal interconnection lines where the polymericor insulating material has a lower dielectric constant (k) then theconventionally used silicon dioxide (SiO₂). Silicon dioxide has adielectric constant of about 3.9 to 4.0. Efforts have been made toreplace silicon dioxide with a material having a dielectric constantlower than about 4.0 and these materials include, for example, thefluorinated oxides which have a dielectric constant of about 3.5.Fluorinated oxides are sometimes described by the acronym FSG, or by thesymbols SiOF and F_(x)SiO_(y). There are a variety of othersilicon-containing low-k materials that are not a fluorinated version ofthe conventionally used silicon dioxide. Carbon-doped glass, or SiOC,has a dielectric constant of about 2.5 to 3.1. The polysiloxanes HSQ,hydrogen silsesquioxane (HSiO_(3/2))_(n) and MSSQ, methyl silsesquioxane(CH₃SiO_(1.5))_(n) have dielectric constants in the range 2.3 to 3.0.These materials are sometimes referred to as spin-on dielectrics(SOD's), or flowable oxides FOx (Dow Corning). Finally, there are low-kdielectric materials that cannot contain silicon, and in fact are eitherpurely organic or substantially organic. Fluorinated amorphous carbon(FLAC, or α-CF), has a dielectric constant in the range 2.3 to 2.7.Polymeric materials include fluorinated poly(arylene ether) (FLARE,Allied Signal), fluorinated polyimide (DuPont), parylene,polyphenylquinoxaline (PPQ), benzocyclobutene (BCB), and the like.Members of this latter group of purely or substantially organicmaterials have dielectric constants in the range of about 2.0 to 3.0.

During back-end processing, that is to say, when the interconnectionsystem is constructed, a problem may occur when silicon based low-kdielectric materials are etched in the presence of oxygen. Such low-kmaterials containing silicon may be more sensitive to oxygen than thepurely organic low-k materials. Oxidation of either HSQ or MSSQ convertsSi—H bonds to Si—OH bonds, which causes the material to absorb moisture,and experience an increase in the dielectric constant. Thus, it isadvantageous to provide a low-k material for back end processing that issubstantially organic and that does not contain silicon as an element.

In an article written by E. Korczynski entitled “Low-k dielectric costsfor dual-damascene integration,” Solid State Technology, May 1999, pp.43-51, it is pointed out that in a fluorinated amorphous carbon film,variously called FLAC, α-CF, and CF_(x), which may be produced byconventional CVD techniques, that by controlling the fluorine to carbonratio in the precursor gases, as well as plasma parameters, theformation of electrically conductive C═C bonds having an sp²hybridization may be eliminated, leading to a film with a lower (andtherefore more desirable) dielectric constant. Furthermore, it is knownin the art to provide a porous version of a low-k dielectric material inorder to achieve a dielectric constant less than about 2(polytetrafluoroethylene, with a dielectric constant of about 2.1, isabout the best achieved so far). This is because a porous dielectricmaterial may be thought of as a composite where the dielectric constantof the air gaps (1.0) reduces the average and the overall dielectricconstant of the material as a whole. Thus, it is desirable to provide amaterial for use in back-end integrated circuit processing that has 1)porosity in the form of air gaps, 2) strong and rigid mechanicalproperties, 3) predominantly sp³ carbon carbon bonding, and optionally4) some degree of fluorine content.

In one embodiment of the present invention, a diamondoid containingmaterial may be used for the low-k layers associated with integratedcircuit multilevel interconnection schemes. An exemplary integratedcircuit for which a diamondoid-containing low-k dielectric layer issuitable is shown schematically in FIG. 9A. This exemplary integratedcircuit is a member of the CMOS technology family (complementary metaloxide semiconductor), where an NMOS (N-type metal oxide semiconductor)device is shown on the right and a PMOS (P-type metal oxidesemiconductor) device is shown on the left. A boron implanted p-typesilicon substrate 901 has a PMOS transistor shown generally at 902fabricated and in n-well 903 of the silicon substrate 901. An NMOStransistor 904 has been fabricated in a p-well 905.

After the transistors have been fabricated on (actually in) the surfaceof the silicon substrate 901, “back-end processing” occurs to constructthe interconnection system that connects individual transistors, such asthe CMOS transistor 902 and the NMOS transistor 904. Two levels of metalinterconnect lines are shown: the first level at 906 and the secondlevel at 907. Metallic vias 908 and 909 serve to vertically connect theupper interconnection level 907 with the lower interconnection level906. As it will be appreciated by those skilled in the art, a dielectriclayer or electrically insulating layer will be deposited to isolate theinterconnect lines located at any one level from one another, as well asfrom interconnection lines or transistor electrode leads from oneanother and from interconnection lines. For example, low-k dielectriclayer 910 insulates interconnection lines at the 906 level from theleads of the 902, 904 transistors. Low-k dielectric layer 911 insulatesinterconnection lines located at the 906 level from one another, as wellas from the interconnect lines located at the 907 level. Additionally,the low-k dielectric layer 911 isolates the vias 908, 909 from oneanother.

According to embodiments of the present invention, the low-k dielectriclayers 910, 911 may comprise any of the diamondoid containing materialsdiscussed above, including a polymerized diamondoid film, adiamondoid-containing ceramic and/or ceramic composite, a CVD depositeddiamondoid-containing film, a CVD diamond film nucleated by diamondoids,or a diamondoid-containing film deposited by self-assembly techniques.In a preferred embodiment, however, the low-k dielectric layers 910, 911comprise a diamondoid-containing polymeric film, which may be a polymersuch as a polyamide or a polyaryl ether. In this embodiment, thediamondoid-polyimide film of FIG. 2C may be used. The polyimide portionof the copolymer illustrated in FIG. 2C may be a fluorinated polyimide,and the diamondoid containing portion of the polymer may containfluorine substituents. Additionally, a diamondoid-containing materialwhich is suitable for low-k dielectric layers 910, 911 may contain airgaps 239 for reducing the overall dielectric constant of the material.As discussed previously, these air gaps 239 may be formed by the sterichindrance created with a large number of diamondoid groups spacedclosely together either within the main chain of the polymer or presentas side groups on the main chain of the polymer. The low-k dielectriclayers 910, 911 may be deposited by conventional spin coatingtechniques, or by CVD methods. In some embodiments, ether linkages suchas those depicted at reference numeral 234, 235 may be desirable toimpact flexibility into the main chain, and facilitate the processing ofthe layer.

According to embodiments of the present invention, the low-k dielectriclayers 910, 911 has a dielectric constant of less than about 4. In apreferred embodiment of the present invention, the dielectric constantof the material is less than about 3. In an even more preferredembodiment of the present invention, the dielectric constant of thematerial is less than about two.

Integrated circuits such as those shown schematically in FIG. 9 may havea top passivation layer 912 that serves to mechanically protect the chipfrom environmental stresses and destructive conditions. In anotherembodiment of the present invention, the passivation layer 912 maycomprise a diamondoid-containing material of the types discussed above,including a polymerized diamondoid film, a diamondoid-containing ceramicand/or ceramic composite, a CVD deposited diamondoid-containing film, aCVD diamond film nucleated by diamondoids, or a diamondoid-containingfilm deposited by self-assembly techniques. The diamondoid comprisingthe IC passivation layer may comprise a derivatized or underivatizeddiamondoid, and it may be either a higher or lower diamondoid, and/orcombinations thereof. If the diamondoid of the passivation layercomprises a higher diamondoid, that diamondoid may be selected from thegroup consisting of tetramantane, pentamantane, hexamantane,heptamantane, octamantane, nonamantane, decamantane, and undecamantane.

In an alternative embodiment, the diamondoid-containing materialsdiscussed above may be used in the dielectric layer of a capacitor,specifically, a capacitor for a static and/or dynamic random accessmemory (SRAM and DRAM, respectively). The capacitor will generally beconfigured as a first and second electrodes with the dielectric layerpositioned between the electrodes. In one embodiment, the diamondoid ofthe diamondoid-containing capacitor dielectric material comprises aderivatized diamondoid; in another embodiment the diamondoid may beunderivatized. The diamondoid may be a higher diamondoid or a lowerdiamondoid, or combinations thereof. If the capacitor dielectric layercomprises a higher diamondoid, the higher diamondoid may betetramantane, pentamantane, hexamantane, heptamantane, octamantane,nonamantane, decamantane, or undecamantane, and combinations thereof.

In a final embodiment of the present invention, a diamondoid ordiamondoid containing material is utilized as a cold cathode filament ina field emission device suitable for use, among other places, in flatpanel displays. The unique properties of a diamondoid make thispossible. These properties include the negative electron affinity of ahydrogenated diamond surface, in conjunction with the small size of atypical higher diamondoid molecule. The latter presents strikingelectronic features in the sense that the diamond material in the centerof the diamondoid comprises high purity diamond single crystal, with theexistence of significantly different electronic states at the surface ofthe diamondoid. These surface states may make possible very longdiffusion lengths for conduction band electrons.

In a chapter entitled “Novel Cold Cathode Materials,” in VacuumMicro-electronics (Wiley, New York, 2001), pp. 247-287, written by W.Zhu et al., the current requirements for a microtip field emitter arrayare given, as well as the properties an improved field emission cathodeare expected to deliver. Perhaps the most difficult problem presented bya conventional field emission cathode is the high voltage that must beapplied to the device in order to extract electrons from the filament.Zhu et al. report a typical control voltage for microtip field emitterarray of about 50-100 volts because of the high work function of thematerial typically comprising a field emission cathode. Diamonds ingeneral, and in particular a hydrogenated diamond surface, offer aunique solution to this problem because of the fact that a diamondsurface displays an electron affinity that is negative.

The electron affinity of the material is a function of electronic statesat the surface of the material. When a diamond surface is passivatedwith hydrogen, that is to say, each of the carbon atoms on the surfaceare sp³-hybridized, i.e., bonded to hydrogen atoms, the electronaffinity of that hydrogenated diamond surface surface can becomenegative. The remarkable consequence of a surface having a negativeelectron affinity is that the energy barrier to an electron attemptingto escape the material is energetically favorable and in a “downhill”direction. Diamond is the only known material to have a negativeelectron affinity in air.

In more specific terms, the electron affinity X of a material isnegative, where X is defined to be the energy required to excite anelectron from an electronic state at the minimum of the conduction bandto the energy level of a vacuum. For most semiconductors, the minimum ofthe conduction band is below that of the vacuum level, so that theelectron affinity of that material is positive. Electrons in theconduction band of such a material are bound to the semiconductor by anenergy that is equal to the the electron affinity, and this energy mustbe supplied to the semiconductor to excite and electron from the surfaceof that material.

It should be noted that a field emission cathode comprising a diamondfilament may suffer from an inherent property: while electrons in theconduction band are easily ejected into the vacuum level, excitingelectrons from the valence band into the conduction band to make themavailable for field emission may be problematic. This is because of thewide bandgap of diamond. In a normal situation, few electrons are ableto traverse the bandgap, in other words, move from electronic states inthe valence band to electronic states in the conduction band. Thus,diamond is generally thought to be unable to sustain electron emissionbecause of its insulating nature. To reiterate, although electrons mayeasily escape into the vacuum from the surface of a hydrogenated diamondfilm, due to the negative electron affinity of that surface, the problemis that there are no readily available mechanisms by which electrons maybe excited from the bulk into electronic surface states.

There may be several ways to circumvent this problem. Observations ofelectron emission from diamond surfaces have either: 1) a high defectdensity, such as a relatively large inclusion of elemental nitrogen, or2) an unusual microstructure including vapor-deposited islands or a filmhaving a nanocrystalline morphology. They can also demonstrate quantummechanically tunneling. It is known in the art that diamond materialswith small grain sizes and high defect densities generally emitelectrons more easily than diamond materials with large crystallinesizes and low defect defect concentrations. It has been reported (seethe Zhu reference above) that outstanding emission properties are seenin ultrafine diamond powders containing crystallites having sizes in therange of 1 to 20 nm. Emission of electrons has been found to originatefrom sites that are associated with defect structures in diamond, ratherthan sharp features associated with the surface, and that compared withconventional silicon or metal microtip emitters, diamond emitters showlower threshold fields, improved emission stability, and robustness andvacuum environments.

According to embodiments of the present invention, a field emissioncathode comprises a diamondoid, a derivatized diamondoid, a polymerizeddiamondoid, and all or any of the other diamondoid containing materialsdiscussed in previous sections of this description. An exemplary fieldemission cathode comprising a diamondoid is shown in FIG. 10.

Referring to FIG. 10, a field emission device shown generally at 1000comprises a diamondoid filament 1001, which acts as a cathode for thedevice 1000, and a faceplate 1002 on which a phosphorescent coating 1003has been deposited. The anode for the device may be either a conductivelayer 1004 positioned behind the phosphorescent coating 1003, or anelectrode 1005 positioned adjacent to the filament 1001. Duringoperation, a voltage from a power supply 1006 is applied between thefilament electrode 1007, and the anode of the device, either electrode1004 or 1005. A typical operating voltage (that is, the potentialdifference between the cathode and the anode) is less than about 10volts. This is what allows the cathode to be operated in a so-called“cold” configuration. A typical electronic affinity for a diamondoidsurface is contemplated to be less than about 3 eV, and in otherembodiments it may be negative. An electron affinity that is less thanabout 3 eV is considered to be a “low positive value.”

Although a diamond material is generally thought to be electricallyinsulating, the diamondoid filament 1001 may be small enough to allowelectrons to tunnel (in a quantum mechanical sense) from the filamentelectrode 1007 to an opposite surface of the diamondoid, which may bethe surface 1008 or the tip 1009. It will be appreciated by the skilledin the art that it is not essential for the diamondoid filament 1001 tohave an apex or tip 1009, since the surface of the diamondoid ishydrogenated and sp³-hybridized. In an alternative embodiment, thesurface of the cathode may comprise a diamondoid-containing materialthat is at least partially derivatized such that the surface comprisesboth sp² and sp³ hybridization.

An advantage of this embodiment of the present invention is that muchgreater resolution of the device may be realized relative to aconventional field emission device because of the small size of atypical diamondoid, derivatized diamondoid, self-assembled diamondoidstructure, or diamondoid aggregate.

Many modifications of the exemplary embodiments of the inventiondisclosed above will readily occur to those skilled in the art.Accordingly, the invention is to be construed as including all structureand methods that fall within the scope of the appended claims.

1. A low-k material for electrically isolating the interconnection linesand vias of an integrated circuit, the low-k material comprising a lowerdiamondoid-containing polymerized material wherein the lower diamondoidis triamantane.
 2. The low-k material of claim 1, wherein the materialcomprises a polymer selected from the group consisting of a polyamide, apolyaryl ether, and a polyimide.
 3. The low-k material of claim 1,wherein the material further contains porosity in the form of air gapsfor reducing the overall dielectric constant of the material.
 4. Thelow-k material of claim 1, wherein the triamantane containing portion ofthe polymer contains fluorine substituents.
 5. The low-k material ofclaim 1, wherein the dielectric constant of the material is less thanabout
 4. 6. The low-k material of claim 1, wherein the dielectricconstant of the material is less than about
 3. 7. The low-k material ofclaim 1, wherein the dielectric constant of the material is less thanabout
 2. 8. The low-k material of claim 1, wherein the weight of thediamondoids as a function of the total weight of the polymer ranges fromabout 1 to 100 percent by weight.
 9. A low-k material for electricallyisolating the interconnection lines and vias of an integrated circuit,the low-k material comprising a higher diamondoid-containing polymerizedmaterial.
 10. The low-k material of claim 9, wherein the higherdiamondoid of the higher diamondoid-containing material is selected fromthe group consisting of tetramantane, pentamantane, hexamantane,heptamantane, octamantane, nonamantane, decamantane, and undecamantane.11. The low-k material of claim 9, wherein the material comprises apolymer selected from the group consisting of a polyamide, a polyarylether, and a polyimide.
 12. The low-k material of claim 9, wherein thematerial further contains porosity in the form of air gaps for reducingthe overall dielectric constant of the material.
 13. The low-k materialof claim 9, wherein the higher diamondoid containing portion of thepolymer contains fluorine substituents.
 14. The low-k material of claim9, wherein the dielectric constant of the material is less than about 4.15. The low-k material of claim 9, wherein the dielectric constant ofthe material is less than about
 3. 16. The low-k material of claim 9,wherein the dielectric constant of the material is less than about 2.17. The low-k material of claim 9, wherein the weight of the diamondoidsas a function of the total weight of the polymer ranges from about 1 to100 percent by weight.
 18. A low-k material for electrically isolatingthe interconnection lines and vias of an integrated circuit, the low-kmaterial comprising a diamondoid-containing polymerized material, thediamondoid-containing portion of the material comprising a mixture oflower and higher diamondoids wherein the lower diamondoid is selectedfrom the group consisting of adamantane, diamantane, and triamantane,and wherein the higher diamondoid is selected from the group consistingof tetramantane, pentamantane, hexamantane, heptamantane, octamantane,nonamantane, decamantane, and undecamantane.
 19. The low-k material ofclaim 18, wherein the material comprises a polymer selected from thegroup consisting of a polyamide, a polyaryl ether, and a polyimide. 20.The low-k material of claim 18, wherein the material further containsporosity in the form of air gaps for reducing the overall dielectricconstant of the material.
 21. The low-k material of claim 18, whereinthe diamondoid containing portion of the polymer contains fluorinesubstituents.
 22. The low-k material of claim 18, wherein the dielectricconstant of the material is less than about
 4. 23. The low-k material ofclaim 18, wherein the dielectric constant of the material is less thanabout
 3. 24. The low-k material of claim 18, wherein the dielectricconstant of the material is less than about
 2. 25. The low-k material ofclaim 18, wherein the weight of the diamondoids as a function of thetotal weight of the polymer ranges from about 1 to 100 percent byweight.
 26. A low-k material for electrically isolating theinterconnection lines and vias of an integrated circuit, the low-kmaterial comprising a diamondoid-containing material selected from thegroup consisting of a diamondoid-containing ceramic, adiamondoid-containing ceramic composite, a CVD diamond film nucleated bydiamondoids, and a film deposited by self-assembly techniques.
 27. Thelow-k material of claim 26, wherein the diamondoid of thediamondoid-containing material is a lower diamondoid selected from thegroup consisting of adamantane, diamantane, and triamantane.
 28. Thelow-k material of claim 26, wherein the diamondoid of thediamondoid-containing material is a higher diamondoid selected from thegroup consisting of tetramantane, pentamantane, hexamantane,heptamantane, octamantane, nonamantane, decamantane, and undecamantane.29. The low-k material of claim 26, wherein the diamondoid of thediamondoid-containing material comprises a mixture of lower and higherdiamondoids, wherein the lower diamondoid is selected from the groupconsisting of adamantane, diamantane, and triamantane, and wherein thehigher diamondoid is selected from the group consisting of tetramantane,pentamantane, hexamantane, heptamantane, octamantane, nonamantane,decamantane, and undecamantane.
 30. The low-k material of claim 26,wherein the diamondoid comprises an underivatized diamondoid.
 31. Thelow-k material of claim 26, wherein the diamondoid comprises aderivatized diamondoid.
 32. The low-k material of claim 26, wherein thematerial further contains porosity in the form of air gaps for reducingthe overall dielectric constant of the material.
 33. The low-k materialof claim 26, wherein the diamondoid containing portion of the polymercontains fluorine substituents.
 34. The low-k material of claim 26,wherein the dielectric constant of the material is less than about 4.35. The low-k material of claim 26, wherein the dielectric constant ofthe material is less than about
 3. 36. The low-k material of claim 26,wherein the dielectric constant of the material is less than about 2.37. The low-k material of claim 26, wherein the diamondoid content ofthe diamondoid-containing material ranges from about 1 to 99.9 percentby weight for the diamondoid-containing ceramic, about 1 to 100 percentby weight for the CVD diamond film nucleated by diamondoids, and about 1to 99.99 percent by weight for the film deposited by self-assemblytechniques.